This invention is particularly useful in the radiation treatment of prostate cancer, among other imaging/treatment applications, and prostate cancer is the focus of this application. It is well known that prostate cancer is a leading cause of death in males, and further that the chances of incurring prostate cancer increase significantly with age. It is also well known that prostate cancer is a complex disease and quite variable, since it can be slow-growing, and hence typically not life-threatening, or it can be very aggressive and fast growing. A number of tests have been developed to attempt to ascertain and differentiate between the slow growing prostate cancers and the significantly more aggressive ones; research continues in this area. It is the aggressive cancers which require prompt treatment; it is advantageous to eliminate the presence of these cancers from the body in the early stages of the cancer and as soon as possible after discovery.
In the treatment of prostate cancer, only a few options have been heretofore available. The most prevalent treatment has been complete removal of the prostate by means of a surgical procedure. However, as with other surgeries, such a procedure is invasive, requires a substantial amount of recovery time, and can have serious complications and side effects, including incontinence and/or impotence. Such serious side effects in many cases deter individuals from treatment or even regular screenings.
Other treatment techniques for prostate cancer include radiation therapy by an externally transmitted beam, which has not proven to be as effective as surgery, and radiation therapy which involves the placement of small radioactive particles, referred to as "seeds", within the prostate. This treatment has proven to be increasingly effective, approximately the same as surgery, as the ability to accurately place the seeds within the prostate has increased. Radioactive seed radiation therapy has the advantage of being relatively non-invasive, less costly, while complications and side effects are less common. A patient is able to leave the hospital/clinic shortly after treatment is completed, and can carry on with normal activities quite soon after.
Success of radiation seed therapy depends upon accurate placement of the radioactive seeds within the prostate. This is generally provided by a stepper assembly which moves an ultrasound probe in a highly controlled manner. The ultrasound probe, mounted on the stepper assembly, is positioned adjacent the prostate, in the rectum of the patient, and as the probe is stepped forward or to the rear, a different slice or plane of the prostate is displayed on the ultrasound monitor. This information is used by the operator to correctly position the radiation seeds in the prostate. The seeds are placed in the prostate by insertion needles which extend through a template mounted on the stepper assembly.
While the ultrasound probe can, with available stepper assemblies, be moved accurately in increments of a desired amount, there is no present capability of providing a known reference position for the successive stepping movement of the probe, apart from moving the entire stepper assembly on a separate mounting element to specifically locate the rear edge of the prostate. Movement of the entire assembly, unless the mounting element includes an expensive adjusting mechanism, can be cumbersome and not very accurate, typically only to within 2-3 millimeters.
It should be understood that, in addition to imaging and treatment of the prostate, stepper assemblies can be used in the imaging and treatment of other human internal organs.
It is thus desirable to have a stepper assembly which is capable of incremental movements of known distance for movement of the ultrasound probe and which is also capable of moving the probe in a continuous, controlled manner independent of the individual stepping movements, so as to provide a reference or base position for the succeeding indexed movements of the stepper and the probe.